Addressing Geologic Challenges Commonly Encountered in Water Infrastructure Tunneling


  • Joshua P. Farmer PE - Hazen and Sawyer

The scope of investigation, implementation during design, and contract execution of a project’s geologic conditions is the single most underestimated/undervalued factor in water and wastewater tunneled/microtunneled/bored crossings in the US. From the most common jack and bores to large scale mechanized water and sewer tunnels, subsurface conditions represent a significant factor to a project’s total cost. However, the collection, interpretation, and contractual execution of subsurface data is rarely efficiently addressed. Most commonly, an engineer and owner apply standardized, “cookie cutter”, approaches to the gathering, interpretation, and contractual inclusion/exclusion of geotechnical data. These inflexible methodologies lead to risk exposure that otherwise would be avoidable or overspending on potentially contractor favorable risk sharing. These increasingly common occurrences arise more prevalently in VA, NC, SC, MD, and DC due to the extreme variety of subsurface conditions found in the Mid-Atlantic States.

In this presentation the speaker will breakout the most significant geologic challenges to water infrastructure tunneling and boring for each of the 3 principal geologic regions of Virginia – Coastal, Piedmont, and Blue Ridge/Appalachian. For each of these regions, the speaker has selected recent, ultimately successful, water infrastructure projects where tunneled crossings encountered significant geologic challenges. The presentation conclusion will focus on lessons learned from the 3 case histories that are now being applied on an ongoing gravity sewer project in Virginia with 10 tunneled/bored crossings of differing constraints.

The attendee can expect the following “takeaways” which should be relatable to their local tunneled/bored crossings – risk reduction and cost savings through phasing of geotechnical investigations, often excluded soil and rock properties pertinent to tunneling methods, explanation of classified/unclassified/baseline contracts, cost saving procedures for soil and rock testing, knowledge gap between project engineer and local geotechnical engineer, and a brief explanation of the common tunneling and boring methods of installation for water infrastructure.

For more information, please contact the author at

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Horizons Fall 2017 (pdf)

Horizons showcases significant water, wastewater, reuse, and stormwater projects and innovations that help our clients to achieve their goals, and can help you achieve yours. Articles are written by top engineers and process group leaders, demonstrating and explaining the beneficial application of a variety of technologies and tools.

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